Concentric line inductance



Dec. 22, 1942. w. H. CONRON' ETAL CONCENTRIC LINE INDUCTANCE Filed March1, 1941 Patented Dec. 22, 1942- CONCENTRIC LINE INDUCTANCE William H.Conron, Haddonfleld, N. J., and Benjamin W. Suckle, Philadelphia, Pa.,assignors to Radio Corporation of America, a corporation of DelawareApplication March 1, 1941, Serial No. 381,214

7 Claims. (01. 178-44) This invention relates to concentric line inductances of the type comprising a center conductor and an outer sleeveconductor joined atone end to form a concentric line inductance andprovided at the opposite end with a tuning capacitor connected betweenthe inner conductor-and the outer conductor. Such a device is disclosedby the U. S. Patent 1,955,093.

When it is desired to cover a frequency range involving a change infrequency of the order of 3 to 1 or greater with a concentric lineinductance in a tunable circuit, it is found that the Q of the circuitis reduced rapidly as the tuning approaches the low frequency end of thetuning range. It is, therefore, an object of this invention to providean improved concentric line tuning inductance for a tunable highfrequency circuit for efiectively covering a relatively wide'frequencyband without impairing the efliciency thereof.

Another object is to .provide a concentric line tuning system comprisinga concentric line element and a variable tuning capacitor foreffectively covering a relatively wide frequency band involving afrequency change of the order of 3 to 1 or greater without loss in thevalue of the Q of the circuit as the tuning approaches the low frequencyend of the range.

It has been found that a relatively wide frequency band or tuning rangemay be divided into two or more overlapping frequency ranges and thetuning may be accomplished with a concentric line inductance byshort-circuiting a portion of the center conductor to the outer'conductor, thereby reducing the inductance of the line. However, sincesuch inductances are utilized in relatively high frequency circuits,slight variations in the length and other constants of the lineordinarily caused by switching means have an amplifying eilect upon thefrequency of the tunable circuit in which the line is utilized.

It is a further object of this invention to proing radial and inparallel. This fact has not heretofore been appreciated in providingvarious expedients for changing the length or inductance of a concentricline tuning system.

It is a further object of this invention to provide a concentric linetuning inductance having a switching means for short-circuiting theinner conductor to the outer conductor at one or more points along theline, thereby to change the length and inductance of the line and animproved switching means for this purpose which may be reset over longperiods of time with extreme accuracy to provide the same inductance ateach resetting.

It is also an object of this invention to provide an improved switchingmeans for a concentric line inductance to short-circuit the innerconductor tp the outer conductorfthereby to adjust the effective lengthof the line at a point between its ends, said switching means providinga multiple path. circuit between said conductors, whereby said circuitsthrough the inner and outer conductors may be maintained in parallel,and to preserve the operatingefficiency of the, line over an extendedoperating period.

The invention will be better understood from the following descriptionwhen considered in connection with the accompanying drawing and itsscope is pointed out in the appended claims.

In the drawing, Figure 1 is a longitudinal view,

. substantially full size and partly in cross section,

vide an improved concentric line tuning inductance provided with meansfor adjusting the ffective length of the inner conductor to cover a,

relatively wide frequency band in tuning, the adjustment of which isaccurate and constant,

and provided with a tuning capacitor at the opposite end provides amultiple path circuit through thejouter conductor from the innerconductcr, thecir cuit elements or current paths beof a concentric linetuning inductance circuit and inductance adjusting means embodying theinvention; and

Figure 2 is a transverse cross sectional view of the inductance changingmeans of Fig. 1, and on the same scale;

Referring to the drawing, the concentric line conductor comprises acenter conductor having a low frequency portion 6 anda high frequencyportion 5 serially connected between a low potential end terminal 1 anda high potential end I sired.

' the input grid 42 of a tube 43.

In the present example, the switch housing contains two spaced outercontact rings I4 and I5 electrically connected directly by clampingmeans I2 to the casing II and, therefore, to the outer conductor andhaving radially inwardly extending spring contact fingers I6 which gripthe periphery of a rotatable contact ring or annular member II, which islocated in a plane normal to the axis of the line between the outer andinner conductors, and provided with radially inwardly projecting spacedblades or contact elements I8.

degrees by an operating handle or lever I9 which projects through a slotin the switching housing I I. In the present example, the contact ringmay be rot ted to the left as viewed in Fig. 2, to carry the b ades I8into engagement between opposed contact fingers 22 and 23 arranged inpairs about the periphery of a flanged head 25 for the high frequencyportion of the inner conductor 5. The fingers are clamped to the flangehead 25 by a clamping ring 26, and extend radially from the head topositions between the blades I8 as shown. When the lever I9 is moved tothe left, contact between the head 25 and the casing II forming part ofthe outer conductor is made through a plurality of radially extendingpaths, thereby maintaining the multiple path circuit of the linecomplete when the inductance is changed. A

The lever I9 represents any suitable operating device for rotating theannular contact member I! through a small angle, and is preferably ofmetal or conducting material whereby it is grounded through the ring tothe outer casing or conductor.

When the switch is open in the position shown, the entire length of theinner conductor is effective with the sections 5 and 6 in series. Inthis position, the capacity between the edges of the blades I8 and thecontacts 2223 is negligible in its effect on the line. Section 6 isconnected to the head 25 by a terminal 28. The low potential terminal Iis connected through a conducting end cover or plate 29 to the outerconductor section III. The head 25 and the terminal 28 are rigidlysupported by insulators 21 which join them respectively to the terminalI and end plate 29.

At the opposite high potential end of the line,

a similar conducting end plate 30 is provided to which is connected oneelement 3| of a variable capacitor 32, and the remaining element orelectrode of the capacitor 33 is connected directly to the flanged end 8of the inner conductor as by a rigid conductor 34. The variablecapacitor shown may be of any suitable type. In the present example, theelement 3| is the rotor, while the element 32 is the stator of the usualrotary variable capacitor having a tuning shaft 35 which ex; tendsthrough the end plate 30 on which the frame 36 is mounted.-

Coupling to the line may be made in any suit- The ring I! is concentricwith theline and is rotatable to a small angle such as 30 able mannerand is here shown as comprising in effect a high potential endconnection 38 on the inner conductor 5 for the anode lead 39 of an am,plifler or oscillator tube 40, and a grid tap 4| at a suitable pointalso on the inner conductor 5, for The tap is made by passing aninsulated grid lead 44 through an opening 45 in the inner conductorwhich is pref-.

erably hollow, as is also the conductor 6, so that the lead may becontinued through the center of the latter conductor to one of aplurality of insulated potential supply terminals 41 secured to thebottom or low potential end or the line, as shown. The plate taplikewise is provided in effeet by the lead 39 at the point 38 where itenters the head 8 of the center conductor. This lead then extendsthroughthe interior of the center conductor to one of the supply terminals 41along with the grid conductor.

Repeated operation of the switch, over a long period of time, does notchange the accuracy of the inductance change, and this is of importancein covering a wide band of frequencies rapidly in tuning, since theinductance change is the same for each resetting of the switch.

We claim as our invention:

1. The combination with a concentric line inductance, of switching meansfor shortening the effective length of the line comprising conductiveelements connecting the inner and outer conductors of said inductancethrough a plurality of substantially equal and uniformly spaced radiallyconducting paths in a plane substantially normal to the axis of theinductance at a point intermediate between the ends thereof, one of saidconducting elements bein movable to interrupt said conducting paths, andmeans controllable externally of said inductance for moving saidlast-named element.

2. The combination with a concentric line comprising an inner centralconductor and an outer conducting sleeve, of a rotary annular contactmember concentric with the line between the inner conductor and outersleeve, means providing a plurality of radial conducting paths betweenthe central conductor and the outer sleeve through said annular contactmember, and means for rotating said contact member selectively toestablish and interrupt said paths.

3. The combination with a concentric line comprising'an inner centralconductor and an outer conducting sleeve, of means for establishing ashort-circuit connection between said sleeve and conductor at a pointintermediate the ends of said line, comprising a rotary ring memberhaving radially inwardly projecting blades lying in a plane normal tothe axis of the line, means providing a flexible connection with theouter sleeve radially about the periphery of said member, and meanscarried by and connected with the inner conductor providing radiallyextending spaced flexible contacts for engaging said blades when saidring member is rotated, thereby to lestablish a plurality of radiallyextending cur-- rent conducting paths between the central conductor andthe outer sleeve.

4. A concentric line inductance comprising in combination, inner andouter conductors, and a switch structure for establishing ashort-circuit connection between said conductors at a point intermediatebetween the ends of said line, comprising an annular rotary conductingelement interposed between said conductors in a plane normal to the axisof the line, said conducting element having inwardly projecting radialspaced blades, contact elements providing a plurality of radialconducting paths between said conducting element and the outerconductor, and a plurality of fixed radial contact elements carried bythe inner conductor and interposed between said blades in spacedrelation thereto for engaging said blades upon rotation of saidconducting element to provide a plurality of radially extending currentconducting paths through said annular member between the inner and outerconductors.

5. A concentric line inductance comprising in combination a centraltubular conductor and an outer concentric conducting sleeve, an annularconducting element interposed between the central conductor and theouter conducting sleeve in a plane normal to the axis of the line, saidconducting element having inwardly projecting radial spaced blades, aplurality of fixed radial contact elements carried by the innerconductor and interposed between said blades in spaced relation theretofor engaging said blades upon rotation of said conducting element toprovide a plurality of radially extending current conducting pathsthrough said annular element between the inner conductor and the outersleeve, means for applying signals to said inductance comprising aninsulated conductor extending through said tubular central conductor,and means for deriving an output potential from said inductancecomprising a second insulated conductor extending through at least aportion of the central con-. ductor;

6. A concentric line inductance, comprising an inner and an outerconductor, a switch housing interposed in and forming part of the outerconductor sleeve, a pair of spaced contact rings carried by the housinghaving radially inwardly extending spring contact fingers, a rotaryannular contact member engaged adjacent its periphery by said springcontact fingers and having radially inwardly projecting spaced blades,means carried by and connected with the inner conductor providingradially extending spaced flexible contacts between saidblades in spacedrelation thereto for engaging the latter when the contact member isrotated, and means extending externally of the housing for rotating saidcontact member to carry the blades into engagement with said flexiblecontacts, thereby to establish a plurality of radially extending currentconducting paths between said conductors.

7. An adjustable concentric line inductance having an inner centralconductor and an outer sleeve conductor, and means for establishing ashort circuit connection between said sleeve and conductor in a planenormal to the axis of the line at a point intermediate the ends of saidline comprising a rotary flat annular member concentric with the linebetween the inner and outer conductors having radially inwardlyprojecting blades, flexible contacts extending radially inwardl'y aboutthe periphery of said annular member providing a plurality of radialconducting paths therefrom to the outer conductor, and a plurality ofradially outwardly extending spaced flexible contacts connected with andcarried by the inner conductor for engaging said blades upon rotation ofsaid annular member from one predetermined position to another, therebyto establish a plurality of radially extending current conducting pathsbetween the inner and outer conductors, and means for rotating saidannular member from one to the other of said positions to adjust theinductance of the line.

WILLIAM H. CONRON. BENJAMIN W. SUCKLE.

